The film begins with the Potter family moving into a new apartment complex in San Francisco. While unpacking, their young daughter Wendy is attacked by a grotesque little creature, who had long ago been transformed from a powerful wizard into a troll. Using a magic crystal green ring, he captures Wendy and possesses her form. After meeting the other eccentric tenants, the family notices Wendy's unusual behavior (roaring, biting, tossing people across rooms, punching people in the groin), but they attribute her behavior to the stress of the move. The only one that notices something is terribly wrong is Wendy's brother, Harry Potter Jr.
Frightened by his sister's sudden and violent changes, he seeks solace in the company of a mysterious old woman named Eunice St. Clair, who lives upstairs. When he tells her of the strange goings-on, she reveals to him her real profession: a witch. Harry asks Eunice to teach him magic, but she says that there isn't time. She does instruct him as to the ways of a hidden magical world, and tells him of her long history stretching back to a time when she and a powerful wizard named Torok were in love. At that time the world was divided between fairies, which includes trolls, and humans. The realms were equal and independent of each other; however, Torok and some of the fairies challenged this balance resulting in a great war in which the humans prevailed. Torok was transformed into a troll as punishment. Eunice stands guard, as she has for centuries now in her apartment, waiting patiently for Torok to challenge the realms again, which is happening now. The troll wizard has already begun his secret war, going from apartment to apartment, attacking the tenants and transforming them into mythical creatures according to their personalities, such as goblins, nymphs, an elf, and a bugbear, and it transforms their rooms into lush fairy worlds. When every apartment is transformed the world of the fairies will burst forth into the world of the humans.
Harry is told by Eunice that Torok can be stopped by plunging a magic staff into the heart of Torok's world. Eunice tells Harry the heart of the new fairy world will be a large and vicious magical creature. Armed with magic staffs which shoot bolts of energy, Eunice and Harry launch a final attempt to stop Torok's hostile takeover of the world and enter the troll's magical alternate universe. Eunice is attacked by Torok and turned into a tree stump, and Harry finds his sister trapped in a coffin of glass à la Snow White. Suddenly, Torok's great bat monster attacks and disables Harry. When it goes after Wendy, Torok kills it, destroying his carefully constructed fairy realm. As the magic world collapses around them, Harry and his family are given a chance to escape, leaving just as the police arrive. Eunice is restored to normal as well as she bids Harry farewell and departs. As the police investigate the house, one of them is drawn into a remaining fragment of the alternate fairy world.
Torok's arm rises into view, preparing to use his ring on the cop. The door closes while the film goes black. The credits roll.Noah Hathaway as Harry Potter Jr.
Michael Moriarty as Harry Potter Sr.
Shelley Hack as Anne Potter
Jenny Beck as Wendy Anne Potter
Sonny Bono as Peter Dickinson
Phil Fondacaro as Malcolm Malory & Torok the Troll
Anne Lockhart as Young Eunice St. Clair
Julia Louis-Dreyfus as Jeanette Cooper
Gary Sandy as Barry Tabor
June Lockhart as Eunice St. Clair
Frank Welker as the voice of Torok the Troll
The estimated budget for Troll was between $700,000 and $1.1 million. Troll opened in the U.S. on January 19, 1986 on 959 screens, earning $2,595,054 that weekend. The film placed ninth on the box office charts for opening weekend.
The film received poor reviews by critics, including by Janet Maslin, Patricia Smith, and Alan Carter. Rex Reed had a few positive comments, but was predominantly negative. Despite the negative response, the film did become a cult classic, and an unrelated 1990 movie initially called "Goblins" was renamed "Troll 2" in an attempt to misleadingly market itself as a sequel to Troll.
Troll was released on a double feature DVD with Troll 2 by MGM on August 26, 2003. Scream Factory released a double feature Blu-ray of Troll and Troll 2 on November 17, 2015. The first 5,000 copies included a DVD of Best Worst Movie, the documentary about the production and legacy of Troll 2.
In 1986, Beck was nominated to 8th Youth in Film Association, for the exceptional performance by a Young Actress.
Troll's plot has no relation to the films Troll 2 or Troll 3, which are intended to be more horror than fantasy. Its first "sequel", Troll 2, produced under the title Goblins, is widely considered to be one of the worst films of all time, and was similarly titled to cash in on the success of the original.
The films Quest for the Mighty Sword (also known as Ator IV, Ator III: The Hobgoblin, or Hobgoblins) and Creepers (also known as Contamination .7 or The Crawlers) both adopted Troll 3 as an alternate title (for the same reason as Troll 2) despite also having no plot relation to previous Troll films (with the exception of the Hobgoblin in Quest resembling the Goblins in Troll 2).
In August 2011, rumors circulated of another sequel. In July 2015, new plans arose in the form of a prequel, titled Troll: The Rise of Harry Potter Jr., along with an animated series. The film, set to star Patricia Arquette and Baxter Bartlett, is set for release in 2017, with the animated series to come in 2018.
Since the release of the Harry Potter books starting in 1997, some of those involved in the film have accused J. K. Rowling of "borrowing" elements from Troll. Producer Charles Band stated in an interview that "there are certain scenes in Troll, not to mention the name of the main character, and this of course predates the Harry Potter books by many years. In 2008, John Buechler's partner in the Troll remake, Peter Davy, said about Harry Potter: "In John's opinion, he created the first Harry Potter. J. K. Rowling says the idea just came to her. John doesn't think so."